This invention relates to an oxygen concentrator, and more particularly to such an oxygen concentrator which may be efficiently switched between its adsorbing and regenerative modes.
Oftentimes, patients with chronic respiratory health problems are required to breath enriched oxygen air for extended periods of time, even when the patients are not hospitalized. As an alternative to the expense and the cumberance of supplying the patient with breathing oxygen from a compressed or liquid oxygen source, oxygen concentrators have come into widespread use for supplying supplemental oxygen to such patients which do not require pure oxygen, but who may breath oxygen-enriched air.
Generally, ambient air consists of about 21 percent oxygen, 78 percent nitrogen, and 1 percent of various trace gases including carbon dioxide and the like. Prior oxygen concentrator apparatus such as is shown in a variety of patents to C. W. Skarstrom, including U.S. Pat. Nos. 2,944,627 and 3,252,268, have been known in which a solid adsorbent has been utilized in an adsorption process to capture and retain a component of a gas mixture passing through the adsorbent bed. Generally, such adsorption apparatus is referred to as a molecular sieve, and a molecular sieve typically comprises a sealed container having a gas inlet and a gas outlet with the container enclosing a suitable adsorbent material bed, depending on the make-up of the gas passing through the molecular sieve. In particular, for use in oxygen concentrating applications, adsorbent beds of zeolite have been most widely used. The gas mixture percolates through the zeolite bed within the molecular sieve container, and a component of the gas mixture (referred to as the adsorbate). nitrogen, is captured and retained by the adsorbing solid or adsorbent. The amount of adsorbate (nitrogen) captured by the adsorbing solid is a semi-continuous, diffusion-limited, surface area-dependent process. After a certain amount of the adsorbate has been adsorbed on the surface of the adsorbing solid, the efficiency of the molecular sieve in adsorbing nitrogen from the superatmospheric air percolating through the molecular sieve decreases markedly.
As is typical in molecular sieve applications, it is necessary, after operating a molecular sieve in its adsorbing mode for a specified length of time, to regenerate the molecular sieve bed. Generally, regeneration of a zeolite bed in oxygen concentration equipment utilizes a purge gas stripping regeneration process in which the nonsorbed gas (oxygen) is utilized to reduce the partial pressure of the adsorbates (nitrogen) adsorbed on the surface of the adsorbate or zeolite bed. In this manner, the sorbed nitrogen on the surface of the adsorbent bed is stripped from the adsorbate and is vented to the atmosphere.After flowing the purging or stripping gas through the adsorbing bed for a sufficient length of time, the bed will have been effectively regenerated.
The process of using zeolite molecular sieves and of alternately operating the molecular sieves in a regenerative and an adsorbing mode is well-known in the art. It is also well-known to utilize a small amount of the oxygen-enriched gas being emitted from the molecular sieve in its adsorbing mode for use as the purging gas forced through the molecular sieve operating in it regenerative mode. However, the pneumatic and timing circuits for controlling the flow of gas through the molecular sieves have been complex and, therefore, expensive.